Synthesis of a 9-Fluorenone Derived β-Amino Alcohol Ligand Depicting High Catalytic Activity and Pronounced Non-linear Stereochemical Effects
作者:Katamreddy Subba Reddy、Lluís Solà、Albert Moyano、Miquel A. Pericàs、Antoni Riera
DOI:10.1055/s-2000-6229
日期:——
The Jacobsen epoxidation of 9-alkylidenefluorenes 4a (ethylidene), 4b (benzylidene) and 4c (1-naphtylmethylene) with standard (R,R)-manganese salen catalyst has been studied. Both conversion and enantioselectivity depend on the steric bulk of the olefin substituent, best results being recorded with 4b (96% yield, 99% ee). The stereochemical course of the epoxidation of 4a is highly dependent on temperature and solvent, the ee of the resulting epoxide (S)-5a varying from 22% (-18°C, CH2Cl2) to 49% (55°C, MTBE). The lithium perchlorate induced ring-opening of 5a with piperidine in MeCN affords a mixture of regioisomeric amino alcohols 3a/2a arising from the amine attack at the more substituted and less substituted carbons, respectively. The 3a/2a ratio can be modulated by the LiClO4 concentration and the reaction temperature, and varies from 44 : 56 to 91 : 9. An independent, completely regio-controlled synthesis of 3a has been developed involving ring-opening by the more substituted carbon of epoxide 5a with diisopropoxytitanium diazide, reduction of azidoalcohol 10a (H2, Pd/C) and cycloalkylation (1,5-dibromopentane, K2CO3) of the amine alcohol 11a. The amino alcohol 3a exhibits a positive nonlinear stereochemical effect in its action as a ligand for the enantioselective addition of Et2Zn to benzaldehyde. The use of regiochemically pure 3a of > 99% ee has been studied in the addition of Et2Zn to a representative family of aldehydes [19 examples, 93.6% mean ee]. The use of the directly available 9 : 1 mixture of 3a and 2a derived from 46-47% ee 5a as a ligand system for the enantioselective addition of Et2Zn to aldehydes [8 examples, 93.1% mean ee] is also reported.
在标准(R,R)-锰沙林催化剂的作用下,研究了 9-亚烷基芴 4a(亚乙基)、4b(亚苄基)和 4c(1-萘亚甲基)的雅各布森环氧化反应。转化率和对映体选择性都取决于烯烃取代基的立体体积,4b 的转化率最高(收率 96%,ee 值 99%)。4a 环氧化反应的立体化学过程高度依赖于温度和溶剂,生成的环氧化物 (S)-5a 的 ee 从 22%(-18°C,CH2Cl2)到 49%(55°C,MTBE)不等。在 MeCN 中,5a 与哌啶在高氯酸锂的诱导下开环,分别在取代度较高和取代度较低的碳上受到胺的侵蚀,从而产生了氨基醇 3a/2a 异构体混合物。3a/2a 的比例可由 LiClO4 浓度和反应温度调节,变化范围为 44 : 56 到 91 : 9。已经开发出一种独立的、完全由区域控制的 3a 合成方法,包括环氧化物 5a 的取代度较高的碳与二异丙氧基重氮化钛的开环反应、叠氮醇 10a 的还原反应(H2、Pd/C)以及胺醇 11a 的环烷基化反应(1,5-二溴戊烷、K2CO3)。氨基醇 3a 在作为 Et2Zn 与苯甲醛的对映体选择性加成的配体时,表现出积极的非线性立体化学效应。在将 Et2Zn 加到具有代表性的醛家族中时,研究人员使用ee > 99% 的区域化学纯 3a [19 例,平均ee为 93.6%]。此外,还报道了使用从逸度为 46-47% 的 5a 直接得到的 9 : 1 的 3a 和 2a 混合物作为配体系统,进行 Et2Zn 与醛的对映选择性加成[8 例,平均逸度为 93.1%]。